Exposure to Smog in Early Pregnancy Linked to Complications

High ozone levels during first trimester may raise risk of preemie birth, preeclampsia, study finds

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WEDNESDAY, Feb. 6, 2013 (HealthDay News) -- Women exposed to elevated levels of ozone air pollution in the first three months of pregnancy may be at increased risk for complications such as preeclampsia and premature birth, a new study suggests.

Mothers with asthma may be most vulnerable, according to the report published in the Feb. 6 online edition of the journal BMJ Open.

Preeclampsia occurs when a woman develops high blood pressure and protein in the urine after the 20th week of pregnancy. Left untreated, it can cause serious complications. Premature birth is delivery before 37 weeks of pregnancy, the study authors noted in the report.

For the study, David Olsson, of the department of public health and clinical medicine at Umea University in Sweden, and colleagues looked at data from nearly 121,000 single-baby pregnancies in Stockholm between 1998 and 2006, as well as air pollution records for the city during that time. Preeclampsia occurred in 2.7 percent of the pregnancies and 4.4 percent of them resulted in a premature birth, the investigators found.

There was no association between levels of vehicle exhaust exposure and pregnancy complications, nor between any air pollutants and low birth weight among the babies, the study authors noted in a journal news release.

However, the researchers did find evidence of a link between exposure to ozone air pollution during the first three months of pregnancy and the risk of preeclampsia and premature birth. The risk for each rose by 4 percent for every 10 micrograms per cubic meter rise in exposure to ozone during the first trimester.

About one in 20 cases of preeclampsia was linked to ozone exposure during early pregnancy, according to the report.

The study also found that mothers with asthma were 10 percent more likely to develop preeclampsia and 25 percent more likely to have a premature birth than those without asthma.

Although the study found an association between first-trimester exposure to high ozone levels and preeclampsia and premature birth, it did not prove a cause-and-effect relationship.